System and method for WLAN OFDMA design of subcarrier groups and frame format

ABSTRACT

Embodiments are provided for WLAN Orthogonal Frequency Division Multiple Access (OFDMA) design of subcarrier groups and corresponding frame format. An embodiment method includes grouping a plurality of subcarriers for OFDMA transmissions into a plurality of subcarrier groups in accordance with a pre-defined grouping structure for subcarriers. The method further includes allocating the subcarrier groups to a plurality of corresponding users, and signaling, to the users, a map of the subcarrier groups to the corresponding users. According to the pre-defined grouping structure, each one of the subcarrier groups includes a plurality of consecutive subcarriers, a plurality of non-consecutive subcarriers, or a combination of consecutive and non-consecutive subcarriers according to a deterministic structure. The map is signaled using an OFDMA PPDU comprising a legacy preamble portion configured to silence legacy users that do not use OFDMA communications, an OFDMA preamble portion indicating the map, and a data portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/325,136, filed on Jul. 7, 2014, which claims the benefit of U.S.Provisional Application No. 61/917,791, filed on Dec. 18, 2013, whichapplications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to network communications, and, inparticular embodiments, to a system and method for Orthogonal FrequencyDivision Multiple Access (OFDMA) design of subcarrier groups and frameformat.

BACKGROUND

Wireless Local Area Networks (WLANs) commonly operate in unlicensedspectrum bands. Rules for operation in these bands force competingdevices to share the available resources and defer their intendedtransmissions when the medium is sensed busy. Typically, a WLAN uses anOrthogonal Frequency Division-Multiplexing (OFDM) transmission format inwhich all transmission resources are assigned to a single device. Randomassignment is commonly achieved using carrier sense multiple access withcollision avoidance (CSMA/CA). With CSMA/CA a device wins access to themedium, transmits its data up to a pre-defined period of time, and thengives up the medium for other devices to compete for transmission. Incontrast, Orthogonal Frequency Division Multiple Access (OFDMA) is atransmission and access mechanism that accommodates multiple-usertransmissions simultaneously. OFDMA is commonly implemented in wirelessinfrastructures operating in the licensed bands in order to meet timinginformation in terms of frame structure and the scheduling of resourcesamong a subset of users. There is a need for efficient schemes forimplementing OFDMA in WLANs.

SUMMARY

In accordance with an embodiment, a method by a network component forprovisioning subcarriers to users for Orthogonal Frequency DivisionMultiple Access (OFDMA) communications in a Wireless Local Area Network(WLAN) includes grouping a plurality of subcarriers for OFDMAtransmissions into a plurality of subcarrier groups. The grouping andthe subcarrier groups are in accordance with a pre-defined groupingstructure for subcarriers. The method further includes allocating thesubcarrier groups to a plurality of corresponding users, and signaling,to the users, a map of the subcarrier groups to the corresponding users.

In accordance with another embodiment, a method by a network componentfor allocating subcarriers to users for OFDMA communications in a WLANincludes establishing a plurality of subcarrier groups for a pluralityof stations (STAs) according to a defined and deterministic groupingstructure for the subcarrier groups, and allocating the subcarriergroups to the STAs. The method further includes establishing a pluralityof user groups. Each one of the user groups represents a sequence of theSTAs. The allocated subcarrier groups are associated with a user groupof the user groups. A sequence of the allocated subcarrier groups withthe user group are then sent to the STAs. The sequence of the STAs ofthe user group is mapped one to one to the sequence of the allocatedsubcarrier groups.

In accordance with another embodiment, a network component forprovisioning subcarriers to users for OFDMA communications in a WLANcomprises a processor and a computer readable storage medium storingprogramming for execution by the processor. The programming includesinstructions to group a plurality of subcarriers for OFDMA transmissionsinto a plurality of subcarrier groups. The grouping and each one of thesubcarrier groups are in accordance with a pre-defined groupingstructure for subcarriers. The programming further includes instructionsto allocate the subcarrier groups to a plurality of corresponding users,and signal, to the users, a map of the subcarrier groups to thecorresponding users.

In accordance with another embodiment, a method by a user devicesupporting OFDMA communications in a WLAN includes receiving anindication of a plurality of subcarrier groups grouping a plurality ofcorresponding subcarriers for OFDMA transmissions. Each one of thesubcarrier groups comprises one or more of the subcarriers. The methodfurther includes receiving an allocation of one of the subcarrier groupsto the user device, and exchanging OFDMA transmissions on one or moresubcarriers belonging to one of the subcarrier groups allocated to theuser device.

In accordance with yet another embodiment, a user device supportingOFDMA communications in a WLAN comprises a processor and a computerreadable storage medium storing programming for execution by theprocessor. The programming includes instructions to receive anindication of a plurality of subcarrier groups grouping a plurality ofcorresponding subcarriers for OFDMA transmissions. Each one of thesubcarrier groups comprises one or more of the subcarriers. Theprogramming includes further instructions to receive an allocation ofone of the subcarrier groups to the user device, and exchange OFDMAtransmissions on one or more subcarriers belonging to one of thesubcarrier groups allocated to the user device.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a WLAN basic service set (BSS);

FIG. 2 illustrates an example of typical assignment of subcarriers tousers in OFDMA;

FIG. 3 illustrates embodiments of subcarrier groupings;

FIG. 4 illustrates an embodiment of an OFDMA physical layer (PHY)Protocol Data Unit (PPDU) for assigning subcarrier groups to users;

FIG. 5 illustrates an embodiment of an OFDMA mapping field forsubcarrier assignment;

FIG. 6 illustrates an embodiment of an OFDMA mapping information element(IE) for subcarrier assignment;

FIG. 7 illustrates an embodiment of a method for assigning subcarriergroups to users in OFDMA WLAN; and

FIG. 8 is a diagram of a processing system that can be used to implementvarious embodiments.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

Disclosed herein are system and method embodiments for WLAN OFDMA designof subcarrier groups and corresponding frame format. The OFDMA designincludes the arrangement of the OFDMA subcarriers into groups and theallocation of groups to different users using a frame format designedfor this purpose. A low-overhead method is also included for allocatingthe subcarriers to different users by grouping the subcarriers intosubcarrier groups.

FIG. 1 shows an example of a WLAN basic service set (BSS) including anaccess point (AP) and one or more stations (STAs). The AP is acommunication device allowing the STAs to access and communicate withthe WLAN. The STAs are any user communication devices allowing users orsubscriber to communicate with the AP and hence the WLAN. Examples ofSTAs include smartphones, tablet computers, laptop computers, desktopcomputers, sensor devices (e.g., smartwatch), and other mobile orcommunication devices with WLAN (e.g., WiFi) capability.

In general, an OFDMA system consists of an integer number ofsubcarriers, N_(sc), defined in a channel of certain bandwidth, WMegahertz (MHz). Each subcarrier represents a sub-range bandwidth or afrequency channel that can be used for uplink and/or downlinktransmissions. For example in WLAN, the bandwidth W is usually set to 20MHz. The subcarrier separation Δf is given by Δf=W/N_(sc). The OFDMAsymbol duration T_(s) is given by 1/Δf. The quantity N_(sc) is set at 64in WLAN OFDM implementation. With the introduction of OFDMA to WLAN,N_(sc) may be set to a higher value, such as 256 or 512 to achieve finergranularity. During each OFDMA transmission (uplink or downlink), anumber of subcarriers are allocated to each of the users participatingin the transmission.

FIG. 2 shows an example of a typical assignment of subcarriers to usersfor general OFDMA transmission. Multiple users are multiplexed in thefrequency domain by assigning a number of subcarriers to each user. Theassignment of subcarriers to each user may be random or in a non-orderlyfashion as shown. The assignment is performed without a defined groupinglogic of subcarriers assigned to a user, in other words without definedstructure for grouping the subcarriers for a user. An assignment of theform shown in FIG. 2 is usually referred to as the map. The map needs tobe propagated to all considered STAs of users indicating whichsubcarriers are assigned to which users. The size of the map can belarge depending on the system parameters since all individualsubcarriers, which are allocated to users, have to be explicitlyrepresented in the map for the allocated symbol durations.

A more efficient scheme for assigning subcarriers in OFDMA is one thatreduces the overhead related to the transmission of the map. In anembodiment, this can be achieved by providing a structured allocation ofthe subcarriers to users in an efficient form. This is achieved bygrouping subcarriers into groups with defined structures. FIG. 3 showstwo embodiments for grouping the subcarriers according to respectivestructures 310 and 320. In structure 310, each group that is assigned toa respective user includes a plurality of consecutive subcarriers. Thegroups may include equal numbers of subcarriers (e.g., 3 subcarriers ateach group as shown) or different quantity of subcarriers as determinedby the network. In structure 320, each group assigned to a respectiveuser includes a plurality of subcarriers dispersed in the spectrum ofavailable subcarriers. The selection of the subcarriers can be based onsome distribution function or some deterministic criteria. Thesubcarriers may be dispersed by a fixed offset of subcarriers (distancesbetween the subcarriers of a group are fixed). The groups may alsoinclude equal or different numbers of subcarriers as determined by thenetwork. The groupings of subcarriers according to the structures 310and 320 are not random but predefined according to any suitabledeterministic criteria. The term deterministic is used herein to referto a non-random grouping approach of the subcarriers into subcarriergroups for users. Further, the AP in the WLAN is responsible forassigning subcarriers to the different subcarrier groups. In anembodiment, this assignment is communicated to associated STAs in acapability element.

With the structured subcarrier grouping, the assignment of subcarriersto users can be done in predefined groups. As such, the group indicesare communicated to users (STAs) rather than the explicit assignment ofeach subcarrier. FIG. 4 shows an embodiment of this assignment.Specifically an OFDMA physical layer (PHY) Protocol Data Unit (PPDU) 400is used for allocating subcarrier groups to users. The OFDMA PPDU 400 issent from a WLAN AP to the considered STAs. For instance STA 1 isassigned subcarrier group 1, STA 2 is assigned subcarrier group 2 and soon. The subcarrier groups can have structures similar to structures 310or 320 above, or other suitable predefined structures. The OFDMA PPDU400 comprises two types of preambles that precede a data portion 410 ofthe OFDMA PPDU 400. The data portion 410 carries data for the STAs, andcan be padded if the amount of data is less than a maximum size of thedata portion. The maximum frame length is determined by the AP or by anOFDMA Coordination Function (OCF) for managing OFDMA resources in theWLAN.

The first preamble 401 is a legacy preamble that can be used to spooflegacy WLAN users that cannot participate in the OFDMA transmission. Theterm legacy herein is used to indicate communications, or communicationspertaining to users, that do not support OFDMA transmission. Such usersneed to keep silence for the duration of the OFDMA transmission. Thissilence duration is indicated in a Legacy Signal Field (L-SIG) of thelegacy preamble. The legacy preamble is transmitted in a WLAN formatthat is commonly referred to as non-High Throughput (non-HT) format. TheLegacy preamble also includes a Legacy Short Training Field (L-STF) anda Legacy Long Training Field (L-LTF) which can be used for thesynchronization and channel estimation, respectively, of the user's dataportion. When there are multiple streams, there is a need to append moreLTFs after the preamble depending on the number of streams.

The format of the data portion 410 can be different than a Legacy dataportion size of an OFDM frame, for instance the Fast Fourier Transform(FFT) frame size for the data portion 410 may be larger than that of theLegacy OFDM frame data portion. In this case, there is no need to useall of the subcarriers (corresponding to one OFDMA symbol) for the LTFs,that is, for training sequences. When the number of training sequencesin the OFDMA PPDU 400 is less than the total subcarrier size for anOFDMA symbol, interpolation may be applied to get the channel estimationfor the entire OFDMA symbol. In this case, the important OFDMA physicallayer (PHY) parameters, including the downlink/uplink map between thetraining sequences may be carried without having a specific Signal (SIG)field for OFDMA PPDUs.

The second preamble 402 of the OFDMA PPDU 400 is an OFDMA preamble. TheOFDMA preamble includes parameters that are relevant to the currenttransmission. These parameters include the coding type, modulation andcoding scheme (MCS), frame length, and possibly other parameters. A STFand LTF can be used for the synchronization and channel estimation,respectively, of the user's data portion. An OFDMA SIG in the secondpreamble 402 (OFDMA preamble) may be divided into two segments, SIG Aand SIG B. The segment SIG A contains general information related to theOFDMA transmission, while SIG B contains information related to eachparticular user. The SIG also carries the mapping of the subcarriergroups to the users.

In an embodiment, to efficiently reduce overhead for carrying themapping information between users and subcarrier groups, a plurality ofuser groups are formed where each user group includes a maximum numberof users, N. The number of predefined subcarrier groups is also madeequal to N. For each user group, each user can be allocated one of the Nsubcarrier groups. Further, a user may appear in a user group more thanone time to allow for the allocation of multiple subcarrier groups to asingle user based on traffic requirements. Each user group is identifiedby a group identifier (GrpID). The GrpID needs to have a sufficientlength (e.g., in number of bits) to satisfy the OFDMA design parameters,such as to allow a maximum number of users that can participate in asingle OFDMA transmission. For instance, the size of the GrpID in bitsis defined to allow a maximum of 4 or 8 users per user group.

FIG. 5 shows an embodiment of an OFDMA mapping field for subcarrierassignment, specifically between user groups (using GrpIDs) andsubcarrier groups. The OFDMA mapping field can be part of the OFDMApreamble (in the SIG field) of an OFDMA PPDU as shown in FIG. 4, andconsists of a GrpID subfield and one or more subcarrier group (SCG)indices. The number of SCG indices in the OFDMA mapping field is equalto the number of users associated with the GrpID. Previous knowledge ofthe GrpID and the position of the user in the user group correspondingto the GrpID is sufficient to indicate which of the subcarrier groups isassigned to which user. The value of GrpID allows the user receiving themapping field to determine the associated user group and hence the orderof the users in that group. The subsequent sequence of subcarrier groups(SCG₁, SCG_(r), . . . , SCG_(s)) in the mapping field provides themapping of the subcarrier groups with the users in the group indicatedby the GrpID value, where the number of the indicated subcarrier groupsis equal to the number of users in the indicated group. The mapping ishence a one to one mapping between the sequence of users in the groupand the sequence of indicated subcarrier groups is used. In addition tothe saving in the overhead related to the map transmission, this mappingapproach allows for the selection of a different group of users, asindicated by the GrpID, per OFDMA transmission.

FIG. 6 shows an embodiment of another mapping approach using an OFDMAmapping information element (IE) for subcarrier assignment. In thisapproach, the transmission of the mapping information can be done usingmanagement frames by defining an IE as shown. The OFDMA mapping IEassociates a STA ID (or a user ID) with a subcarrier group index. TheSTA ID can be a MAC address or an association ID (AID) assigned by theAP to the STA during association. Since an IE may have more bits thanneeded for the mapping, other subcarrier information such as modulationand coding information may also be included in the IE. While moreinformation can be transported using this approach, users participatingin the OFDMA TXOP may be limited to a fixed set of users during theentire TXOP.

FIG. 7 shows an embodiment of a method 700 for assigning subcarriergroups to users in OFDMA WLANs. At step 710, the AP or an accesscontroller (AC) of the WLAN establishes a plurality of subcarrier groupsfor a plurality of corresponding STAs according to a deterministicgrouping structure. For instance, a plurality of consecutive subcarriersin an available bandwidth of subcarriers (e.g., 20 MHz) is designatedfor each group that corresponds to a user, e.g., similar to thestructure 310 above. Alternatively, for each STA, the subcarriers aredistributed in the bandwidth such as no consecutive subcarriers areassigned to an STA. At step 720, the assignment is signaled to the STAs,e.g., by the AP, in a data portion of an OFDMA PHY PPDU (as shown inFIG. 4), using an OFDMA mapping field (as shown in FIG. 5), using anOFDMA mapping IE (as shown in FIG. 6), or other suitable means ofmapping subcarrier groups to users. In the case of using the dataportion of the OFDMA PHY PPDU, the mapping between STAs and SCGs can beexplicit. In the case of using the OFDMA mapping field, the mapping isbetween user group IDs and a sequence of SCGs, as described above. Inthe case of using the OFDMA mapping IE, each user STA is explicitlymapped to a predefined subcarrier group by signaling the STA ID and thesubcarrier group index. When a STA or user device receives theassignment, the STA can use this information to decide which subcarriergroup is assigned to it, and hence determine the subcarriers belongingto that subcarrier group for exchanging OFDMA communications.

FIG. 8 is a block diagram of a processing system 800 that can be used toimplement various embodiments. For instance the processing system 800can be part of an AP, a STA, or an AC in a WLAN. Specific devices mayutilize all of the components shown, or only a subset of the components,and levels of integration may vary from device to device. Furthermore, adevice may contain multiple instances of a component, such as multipleprocessing units, processors, memories, transmitters, receivers, etc.The processing system 800 may comprise a processing unit 801 equippedwith one or more input/output devices, such as a speaker, microphone,mouse, touchscreen, keypad, keyboard, printer, display, and the like.The processing unit 801 may include a central processing unit (CPU) 810,a memory 820, a mass storage device 830, a video adapter 840, and an I/Ointerface 86 o connected to a bus. The bus may be one or more of anytype of several bus architectures including a memory bus or memorycontroller, a peripheral bus, a video bus, or the like.

The CPU 810 may comprise any type of electronic data processor. Thememory 820 may comprise any type of system memory such as static randomaccess memory (SRAM), dynamic random access memory (DRAM), synchronousDRAM (SDRAM), read-only memory (ROM), a combination thereof, or thelike. In an embodiment, the memory 820 may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms. In embodiments, the memory 820 is non-transitory. The massstorage device 830 may comprise any type of storage device configured tostore data, programs, and other information and to make the data,programs, and other information accessible via the bus. The mass storagedevice 830 may comprise, for example, one or more of a solid statedrive, hard disk drive, a magnetic disk drive, an optical disk drive, orthe like.

The video adapter 840 and the I/O interface 860 provide interfaces tocouple external input and output devices to the processing unit. Asillustrated, examples of input and output devices include a display 890coupled to the video adapter 840 and any combination ofmouse/keyboard/printer 870 coupled to the I/O interface 860. Otherdevices may be coupled to the processing unit 801, and additional orfewer interface cards may be utilized. For example, a serial interfacecard (not shown) may be used to provide a serial interface for aprinter.

The processing unit 801 also includes one or more network interfaces850, which may comprise wired links, such as an Ethernet cable or thelike, and/or wireless links to access nodes or one or more networks 880.The network interface 850 allows the processing unit 801 to communicatewith remote units via the networks 880. For example, the networkinterface 850 may provide wireless communication via one or moretransmitters/transmit antennas and one or more receivers/receiveantennas. In an embodiment, the processing unit 801 is coupled to alocal-area network or a wide-area network for data processing andcommunications with remote devices, such as other processing units, theInternet, remote storage facilities, or the like.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method for provisioning subcarriers fororthogonal frequency division multiple access (OFDMA) communications toa plurality of stations (STAs) in a wireless local area network (WLAN),the method comprising: signaling, by a network component to theplurality of STAs, a physical layer (PHY) protocol data unit (PPDU)comprising: a first preamble portion, which is a legacy preamblecomprising a Legacy Short Training Field (L-STF), a Legacy Long TrainingField (L-LTF), and a Legacy Signal Field (L-SIG) in a non-HighThroughput (non-HT) format; and a second preamble portion, prior to anyuser data in the PPDU, and comprising a short training field (STF)providing synchronizing information, a long training field (LTF)providing channel estimation information, and a signal (SIG) fieldincluding an OFDMA mapping field for mapping subcarrier groups to theplurality of STAs according to a predefined and deterministic groupingstructure.
 2. The method of claim 1, each of the subcarrier groupsincluding a plurality of consecutive subcarriers in accordance with thepredefined and deterministic grouping structure.
 3. The method of claim1, each of the subcarrier groups including a same number of subcarriersin accordance with the predefined and deterministic grouping structure.4. The method of claim 1, at least some of the subcarrier groupsincluding a different number of subcarriers from each other inaccordance with the predefined and deterministic grouping structure. 5.The method of claim 1, the subcarriers in each of the subcarrier groupsoffset by a same number of other subcarriers in accordance with thepredefined and deterministic grouping structure.
 6. The method of claim1, the PPDU further comprising a data portion after the second preambleportion.
 7. The method of claim 1, wherein the mapping is a one to onemapping between a sequence of STAs and a sequence of indicatedsubcarrier groups.
 8. The method of claim 1, the first preamble portionhaving a different Fast Fourier Transform (FFT) frame size than thesecond preamble portion for OFDMA communications.
 9. An apparatus forprovisioning subcarriers for orthogonal frequency division multipleaccess (OFDMA) communications to a plurality of stations (STAs) in awireless local area network (WLAN), the apparatus comprising: a memory;and a transmitter configured to signal, to the plurality of STAs, aphysical layer (PHY) protocol data unit (PPDU) comprising: a firstpreamble portion, which is a legacy preamble comprising a Legacy ShortTraining Field (L-STF), a Legacy Long Training Field (L-LTF), and aLegacy Signal Field (L-SIG) in a non-High Throughput (non-HT) format;and a second preamble portion, prior to any user data in the PPDU, andcomprising a short training field (STF) providing synchronizinginformation, a long training field (LTF) providing channel estimationinformation, and a signal (SIG) field including an OFDMA mapping fieldfor mapping subcarrier groups to the plurality of STAs according to apredefined and deterministic grouping structure.
 10. The apparatus ofclaim 9, wherein each of the subcarrier groups includes a plurality ofconsecutive subcarriers in accordance with the predefined anddeterministic grouping structure.
 11. The apparatus of claim 9, whereineach of the subcarrier groups includes a same number of subcarriers inaccordance with the predefined and deterministic grouping structure. 12.The apparatus of claim 9, wherein at least some of the subcarrier groupsinclude a different quantity of subcarriers from each other inaccordance with the predefined and deterministic grouping structure. 13.The apparatus of claim 9, wherein the subcarriers in each of thesubcarrier groups are offset by a same number of other subcarriers inaccordance with the predefined and deterministic grouping structure. 14.The apparatus of claim 9, the PPDU further comprising a data portionafter the second preamble portion.
 15. The apparatus of claim 9, whereinthe mapping is a one to one mapping between a sequence of STAs and asequence of indicated subcarrier groups.
 16. The apparatus of claim 9,wherein the first preamble portion has a different Fast FourierTransform (FFT) frame size than the second preamble portion for OFDMAcommunications.
 17. A method for orthogonal frequency division multipleaccess (OFDMA) communications in a wireless local area network (WLAN),the method comprising: receiving, by a station (STA), a physical layer(PHY) protocol data unit (PPDU) comprising: a first preamble portion,which is a legacy preamble comprising a Legacy Short Training Field(L-STF), a Legacy Long Training Field (L-LTF), and a Legacy Signal Field(L-SIG) in a non-High Throughput (non-HT) format; and a second preambleportion, prior to any user data in the PPDU, and comprising a shorttraining field (STF) providing synchronizing information, a longtraining field (LTF) providing channel estimation information, and asignal (SIG) field including an OFDMA mapping field for mappingsubcarrier groups to a plurality of STAs according to a predefined anddeterministic grouping structure; and exchanging, by the STA, OFDMAtransmissions on one or more subcarriers belonging to one of thesubcarrier groups allocated to the STA.
 18. The method of claim 17, eachof the subcarrier groups including a same number of subcarriers inaccordance with the predefined and deterministic grouping structure. 19.The method of claim 17, at least some of the subcarrier groups includinga different number of subcarriers from each other in accordance with thepredefined and deterministic grouping structure.
 20. The method of claim17, the subcarriers in each of the subcarrier groups offset by a samenumber of other subcarriers in accordance with the predefined anddeterministic grouping structure.
 21. The method of claim 17, whereinthe PPDU further comprises a data portion after the second preambleportion.
 22. The method of claim 17, wherein the mapping is a one to onemapping between a sequence of STAs and a sequence of indicatedsubcarrier groups.
 23. The method of claim 17, the first preambleportion having a different Fast Fourier Transform (FFT) frame size thanthe second preamble portion for OFDMA communications.
 24. An apparatussupporting orthogonal frequency division multiple access (OFDMA)communications in a wireless local area network (WLAN), the apparatuscomprising: a memory; a receiver configured to receive a physical layer(PHY) protocol data unit (PPDU) comprising: a first preamble portion,which is a legacy preamble comprising a Legacy Short Training Field(L-STF), a Legacy Long Training Field (L-LTF), and a Legacy Signal Field(L-SIG) in a non-High Throughput (non-HT) format; and a second preambleportion, prior to any user data in the PPDU, and comprising a shorttraining field (STF) providing synchronizing information, a longtraining field (LTF) providing channel estimation information, and asignal (SIG) field including an OFDMA mapping field for mappingsubcarrier groups to plurality of STAs according to a predefined anddeterministic grouping structure; and the receiver and/or a transmitterconfigured to exchange OFDMA transmissions on one or more subcarriersbelonging to one of the subcarrier groups allocated to the STA.
 25. Theapparatus of claim 24, wherein each of the subcarrier groups includes asame number of subcarriers in accordance with the predefined anddeterministic grouping structure.
 26. The apparatus of claim 24, whereinat least some of the subcarrier groups include a different number ofsubcarriers from each other in accordance with the predefined anddeterministic grouping structure.
 27. The apparatus of claim 24, whereinthe mapping is a one to one mapping between a sequence of STAs and asequence of indicated subcarrier groups.
 28. The apparatus of claim 24,wherein the subcarriers in each of the subcarrier groups is offset by asame number of other subcarriers in accordance with the predefined anddeterministic grouping structure.
 29. The apparatus of claim 24, whereinthe PPDU further comprises a data portion after the second preambleportion.
 30. The apparatus of claim 24, wherein the first preambleportion has a different Fast Fourier Transform (FFT) frame size than thesecond preamble portion for OFDMA communications.